1. Field of the Invention
The present invention is in the field of the refrigerators and in particular, relates to commercial upright type refrigerators. The present invention is an improved door mounting frame structure for such refrigerators.
A refrigerated cabinet door and door mounting frame structure system is shown in U.S. Pat. No. 3,724,129 to Stromquist, issued Apr. 3, 1973. In essence, there is shown a refrigerated cabinet or room having a rectangular opening in one of its vertical walls. A door mounting frame structure is inserted within this opening, and the vertically hinged doors are mounted within the frame structure. Generally, the frame structure and the door frames are made of metal because of the durability and appearance of that material and the ease with which it may be manufactured. Most metals, however, are superior conductors of heat.
If preventive measures were not taken, the metalic door mounting frames and to some extent the door frames themselves would tend to operate at a temperature at or below the dew point of the air outside of the refrigerator. Under conditions of high humidity, condensation and frost can form. These effects are undesirable, not only because they detract from the appearance and the safety of the doors, but also because they graphically show a considerable waste of energy.
To prevent condensation and frost from forming on the door mounting frame structure, it has become the practice to provide a submerged electrical heating wire located within the door mounting frame structure which, when supplied with electrical current generates a small amount of heat, adequate to prevent condensation. U.S. Pat. No. 3,612,821 to Stromquist issued Oct. 12, 1971 illustrates the manner in which the electrical heating wires are arrayed within the door mounting structure. Although the use of the heater wires does not consume a large amount of energy relative to the total energy consumed by most refrigerators, nevertheless it is desirable to conserve energy by providing a door frame mounting structure which is thermally as efficient as possible.
The structure described in U.S. Pat. No. 3,612,821 includes several portions. A first portion generally slightly below ambient temperature extends from the outside of the refrigerator inward forming a door jamb. A second portion extends perpendicular to the first (jamb) portion and parallel to the wall of the refrigerator, forming a door buck portion. The end of the buck portion opposite the jamb portion is in contact with the cold air inside the refrigerator.
The intermediate part of the buck portion is provided with a sealing surface against which the magnetic sealing gasket of the door seats, preventing the flow of air between the door and the door frame. Because this sealing area is adjacent the coldest part of the door mount frame, the problem of condensation and frosting is particularly acute in that area. For this reason, a heater element is usually located there.
Condensation cannot form on a surface which is maintained at a temperature above the dew point temperature of the air next to the surface. The dew point temperature depends strongly on the relative humidity of the air, but never exceeds the temperature of the air. For this reason, the temperature of the heated area is maintained above the dew point, between room temperature and the temperature of the interior of the refrigerator.
Nilsen in U.S. Pat. No. 3,204,324 issued Sept. 7, 1965, shows a method for producing an insulating construction or structural member for use in windows, wall panels, ventilators, mullions and the like, wherein the structural members on the exterior and interior of the walls are separated by an insulating spacer.
That method includes providing originally a metal strip having a channel into which solidifiable insulative material is poured and allowed to solidify, then removing a part of the original strip forming the channel. This leaves a final strip consisting of two parts of the original strip bonded to the insulative material but spaced apart from each other by it, whereby the thermally conductive path between the two parts is interrupted by the insulative material.
Holliday and Barker in U.S. Pat. No. 3,624,885 issued Dec. 7, 1971 describe a machine for producing the type of insulated structural member described in Nilsen.
Inserting an insulative section between the portion of the door mounting frame outside the refrigerator and the portion extending into the refrigerator would reduce the flow of heat from the outside ambient environment into the refrigerator interior. A large thermal gradient would exist across the insulative section, with the result that the sealing surface and other parts of the frame exposed to the air outside the refrigerator would be maintained at a temperature below the dew point. As a result, condensation and frosting would be a problem. One way to relieve this problem is to provide localized electrical heating in the area of the sealing surface.
Providing a given level of electrical heating in an insulated door frame structure has the effect of maintaining the portion of the door buck portion nearest the insulative section at a temperature lower than it would be if the insulation were not present. The overall heat load on the refrigerator is not necessarily less than it would be if the insulative section were not present because the heater must supply the heat required to elevate a section of the buck portion above the dew point. Thus, it does not appear efficient to provide electrical heating in an insulated door frame structure.
If a non-insulated door mounting structure is provided with an electrical heater wire as shown in U.S. Pat. No. 3,612,821, it would appear that no further advantage could be obtained by thermally isolating the part of the structure extending into the refrigerator from the part of the structure outside the refrigerator. The presence of the heater element between those parts decreases the thermal gradient between the part outside the refrigerator and the heater element while increasing the thermal gradient between the heater element and the part of the structure extending into the refrigerator. As a result, the flow of heat from the outside is retarded, much as it would be by insulation, while the flow of heat from the heater element to the interior of the refrigerator is augmented. In fact, adding insulation between the part outside the refrigerator and the area near the heater element would be detrimental, because otherwise the heat flowing into the area of the heater element from outside could assist in the prevention of condensation and frost in that area. Thus, it does not appear reasonable to add an insulative section to a non-insulated door mounting frame containing an electrical heater element.
From the above discussion it appears that the use of an insulative thermal barrier and the use of an electrically heated area are inconsistent approaches, and it is not obvious how the advantages can be obtained simultaneously.